Among the high profile entries in Toronto's 2007 Film Fest was Ang Lee's "Lust, Caution" which had particular notoriety. Not only were fest-watchers waiting to confirm or contradict the early mixed reaction from the Venice Film Festival where it won the Golden Lion, but they were curious to see what earned this erotic thriller its NC-17 rating.

Ang Lee, the Award-winning director of "Brokeback Mountain" and "Crouching Tiger, Hidden Dragon," brings a startling and erotic espionage thriller about the fate of an ordinary woman's heart. It is based on a short story by revered Chinese author Eileen Chang and stars Asian cinema icon Tony Leung opposite screen newcomer Tang Wei.

A period drama set in Shanghai in 1942, the World War II Japanese occupation of this Chinese city continues in force. Mrs. Mak, a woman of sophistication and means, walks into a cafˇ, places a phone call, and then sits and waits. She remembers...

We then go back four years to when she was still known as Wang Jiazhi, a young college freshman roped into joining the drama department as they put on a play to support the resistance against invading Japanese troops. She proves to be a natural and when the drama students led by Kuang Yu Min get riled up over Chinese traitors collaborating with the invading Japanese, she's enlisted in their plan to kill one of the main Hong Kong offenders, Mr. Yee - having her cozy up to his wife and join her mah-jong circle. She ultimately winds up having an affair with the man they want to kill, making it even harder for her to fulfill the mission. Wong transforms herself utterly inside and out, and the events proceed as scripted - until an unexpectedly fatal twist spurs her to flee.

Cut to Shanghai, 1941, a year before the feature's first chapter began. With no end in sight for the occupation, Wong, having emigrated from Hong Kong, goes through the motions of survival. To her surprise, Kuang reenters her life. Now part of the organized resistance, he enlists her to again become Mrs. Mak in a revival of the old plot to kill Yee. In the intervening years, as head of the collaborationist secret service, Yee has become a crucial member of the puppet government. As Wong reprises her earlier role, and is drawn closer to her dangerous prey, she finds her very identity tested and pushed to the limit.

Leung and Tang generate sparks and chemistry, especially in the sex scenes, which are bold by any standards as they involve full-frontal female nudity and unconventional sexual positions. Ang Lee stages them with meticulous attention to detail, imbuing each encounter with emotional intensity as well as eroticism.

If you're a fan of period films, you might appreciate Ang Lee's effort to create a traditional Chinese tale. Some might find the ending to be a bit of a disappointment especially since it might not go the way some might expect.

Opens in San Francisco on Friday, October 5. Bay Area on Friday, October 12.Rated; NC-17/ Running time 158 mins.